(core) Floating formula editor

Summary:
Adding a way to detach an editor. Initially only implemented for the formula editor, includes redesign for the AI part.
- Initially, the detached editor is tight with the formula assistant and both are behind GRIST_FORMULA_ASSISTANT flag, but this can be relaxed
later on, as the detached editor can be used on its own.

- Detached editor is only supported in regular fields and on the creator panel. It is not supported yet for conditional styles, due to preview limitations.
- Old code for the assistant was removed completely, as it was only a temporary solution, but the AI conversation part was copied to the new one.
- Prompting was not modified in this diff, it will be included in the follow-up with more test cases.

Test Plan: Added only new tests; existing tests should pass.

Reviewers: JakubSerafin

Reviewed By: JakubSerafin

Differential Revision: https://phab.getgrist.com/D3863

app/client/widgets/ConditionalStyle.ts

@@ -200,6 +200,7 @@ export class ConditionalStyle extends Disposable {
           editRow: vsi?.moveEditRowToCursor(),
           refElem,
           setupCleanup: setupEditorCleanup,
+          canDetach: false,
         });
         // Add editor to document holder - this will prevent multiple formula editor instances.
         this._gristDoc.fieldEditorHolder.autoDispose(editorHolder);